Johann Schröter

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Johann Schröter

(extended biography)


The lunar crater Schröter, the nearby rille Rima Schröter, and the unrelated valley Vallis Schröteri are named after Johann Hieronymus Schröter (August 30, 1745 – August 29, 1816), a German planetary astronomer and selenographer. Schröter is in many ways the father of modern telescopic studies of lunar details.

Career

Schröter, then a rising young lawyer attached to the Prussian court, is said to have been so electrified by Sir William Herschel’s discovery of Uranus in 1781, that he managed to have himself appointed magistrate of the small north German town of Lilienthal, near Bremen; so that a lighter load of official duties would leave him with the leisure to devote most of his time to astronomy, an interest he had been pursuing for the previous two years.
 
  Beginning the following year Schröter set up an elaborate private observatory, starting with reflecting telescopes of 4.75 and 6.5 inches, frabricated by Sir William himself, to which he later added, in 1792, a 9.5 inch Schrader reflector, and, shortly thereafter, one of either 18.5 or 20-inches aperture -- at that time the largest in continental Europe. As his skills developed he became the preeminent planetary astronomer of the time, and was later called (by Agnes Clerke) “the Herschel of Germany” and (by Joseph Ashbrook) “the Percival Lowell of his age” (like Lowell, Schröter had a strong belief in the likelihood of life on other planets).
 
  Schröter’s career ended tragically on April 20, 1813 when Lilienthal was sacked by French troops. Some accounts say Schröter’s observatory, and most of his papers, were burned; others say they were untouched.
 
  In addition to his own legacy Schröter was instrumental in launching the careers of Harding and Bessel, both of whom served him as assistants.

Lunar Contributions

  • Although not exclusively a lunar observer, Schröter’s ambitious personal plan for lunar studies, built around Tobias Mayer’s system of accurate feature positions, was to (according to Whitaker, p. 98):
    • observe and delineate lunar features under all conditions of illumination
    • measure the heights and depths of the most important elevations and craters
    • look for evidence of a lunar atmosphere and changes on the surface
    • produce a complete map of the Moon 46.5 inches in diameter, to replace Mayer’s.
  • Schröter’s plan for a new atlas was never completed, however approximately 75 plates of selected regions and near the planned scale were published, along with explanatory text in the two volumes of his Selenotopographische Fragmente zur genauern Kenntniss der Mondfläche which appeared in 1791 and 1802 (the second volume five years after its completion).
  • Schröter, as had others, attempted to reconcile Hevelius’s names with Riccioli’s, choosing the latter for this maps, and adding many of his own. He also seems to have introduced the system of identifying secondary features with letters, both Latin and Greek, although he does not seem to have used them in a systematic or even consistent way (using different letters for the same feature on different maps).
  • Schröter is also credited with introducing the terms rille and crater and initiating the trend away from Latin names (Whitaker, p. 106)


Publications

  • Schröter, Johann Hieronymus. 1791/1797/1802. Selenotopographische Fragmente zur genauern Kenntniss der Mondfläche, ihrer erlittenen Veränderungen und Atmosphäre, sammt den dazu gehörigen Specialcharten und Zeichnungen. Lilienthal: Auf Kosten des Verfassers.
    • Schröter's book was published in two volumes. According to Sheehan and Baum (below), Volume 2 was completed in 1797 and the two volumes were republished as a set in 1802.
    • What appears to be a complete electronically searchable scan of the text of Harvard College's copy, once owned by Thomas Elger, of Volume 1 (but without the illustrations) can be found on Google Books.
    • Seventy plates from Volumes 1 and 2 (beginning with Schröter's revision of Tobias Mayer's map) can be found on Gallica. The plates are labeled T V through T LXXV, "T" apparently being an abbreviation for the Latin Tabula (meaning "plate" or "engraving"). Plates 1-4, and the text, are not reproduced.
    • Excellent (but not electronically-searchable) scans of both volumes of Selenotopographische Fragmente, including the plates, are available for viewing (or PDF downloading) from the Swiss ETH's e-rara rare book web resource.
    • Both volumes were reportedly also reproduced as part of the Landmarks of Science microfiche collection.
    • A moderately large copy of Schröter's version of Mayer's map can be found in Whitaker, on pp. 102 and 103. The zoomable version from the ETH is even clearer.
  • Schroeter, John Jerome. 1792. "Observations on the atmospheres of Venus and the Moon, Their Respective Densities, Perpendicular Heights, and the Twi-Light Occasioned by Them." Philosophical Transactions of the Royal Society of London, Vol. 82, pp. 309–361.
    • This article (translated into English) about twilight on Venus includes observations of the lunar cusps repeated in Vol. 2 of the Selenotopographische Fragmente. It refers specifically to the cusp observations in Figures 1-3 of Plate T. LXV, where the area "c".."k" (in Figures 1 and 2) denotes a "pyramid of light" that Schröter claimed to have observed at both poles and interpreted as a twilight effect related the lunar atmosphere. Schröter felt the immediate vicinity of the poles was brighter than the remainder of the area lit by Earthshine alone, as evidenced by the limb first becoming visible there as the Earth's evening sky darkened.
    • The text of this article can be found in an abridged version of the Transactions on Google books.


Additional Information

  • According to Neison, 1876 (page 95), Schröter's many measurements of libration and shadow lengths were made by mental comparison with the grid on a ruled paper placed so that it could be viewed with one eye while looking through the telescope with the other -- a technique pioneered by Galileo Galilei, and called a "projection machine" by Schröter. Evidently Beer and Mädler (who used an eyepiece micrometer for the same purpose) disparaged the apparent crudeness of Schröter's method, but it can actually work quite well, the images presented to the two eyes being seen superimposed in the observers' mind. The measurements affixed to Schröter's drawings and mentioned in his text appear quite reliable. His raw measurements are reported in "lines," and he generally equates 1 line to 4 arc-seconds in the sky. According to Neison, the projection machine consisted of a 1/2-inch paper grid viewed at a distance of 32.5 inches. This would give a visual reference scale of 0.88° or 3173 arc-sec per line. For the telescopic image to be seen at a scale of 4 arc-seconds per line, the magnification in the telescope would have to be 3173/4 = 793X. Since that is much higher than the powers mentioned by Schröter (at least in Vol. 1 of his book), there seems to be something wrong with Neison's description of the projection machine. One also has to assume Schröter had some mechanism to adjust the distance to compensate for the differences in magnification produced by the various telescopes and eyepieces he used, especially in Vol. 2.



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